A seed’s successful transition to a seedling depends on the suitability of the surrounding environment into which it is dispersed. All plants require water, sunlight, favorable temperatures, and soil nutrients to survive. Biotic interactions, such as competition, herbivory, and disease also impact survival. The goal of this study is to determine which factors influence tree germination and survival in Washington State’s temperate forests. Are there essentials without which seeds fail to complete the pivotal transition between embryo and tree? This question was explored through four years of data from a 25.6 hectare plot located in the Gifford Pinchot National Forest. The seeds of the plot’s dominant trees, including Western hemlock and Douglas fir, were the focus of this study. Seed densities in the plot were quantified using seed traps, which collect falling seeds at regular spatial intervals. Germinants, seedlings, and environmental data were recorded within a square meter quadrat adjacent to each seed trap. Regression analyses were used to determine whether germination rates (proportion of seeds that complete the transition to seedlings) and seedling survival were influenced by climatic factors, other organisms, seed densities, or annual variation.
Results/Conclusions
Due to its dominance within the stand, only seeds from Tsuga heterophylla (Western hemlock) were numerous enough to produce statistically significant patters. Results thus far show that germination rates for this species are not determined by variations in soil moisture and sun exposure. In addition, germination rates appear to be negatively correlated with nearby vegetation cover, and positively correlated with nurse log cover. The negligible role of moisture and sunlight is surprising, considering their importance in plant growth. This suggest that other factors, such as vegetation and nurse log cover, are the primary drivers of germination success. High seed quantities from 2017 samples indicate that this was a mast year, which provides an interesting new opportunity to see if masting influences germination rate. Germination is an important and delicate life stage for every tree, and through their influence on it environmental factors may shape the species composition of these communities. Identifying important environmental factors may grant insight into how certain species take advantage of disturbance, respond to competition, or tolerate fluctuations in climate. This may also provide some ability to anticipate how these trees will respond to the warmer and dried conditions expected to define climate change in Washington.